Bug Description

How to reproduce:
1. open network settings in gnome-control-center
2. set proxy like the example below:
* method - manual
* HTTP Proxy - example.com:8080
* HTTPS Proxy - example.com:8090
3. press "Apply system wide"
- confirm proxy settings are written in /etc/apt/apt.conf
4. add the line below into /etc/apt/apt.conf manually
- Acquire::http::proxy::server1.local "DIRECT";
5. add the line below into /etc/apt/apt.conf.d/90no-proxy.conf
- Acquire::http::proxy::server2.local "DIRECT";
6. turn off proxy by set back the Method to "None" and press "Apply system wide" again.

Expected to happen:
7. the three lines below are removed from /etc/apt/apt.conf
- Acquire::http::proxy "http://example.com:8080/";
- Acquire::https::proxy "http://example.com:8080/";
- Acquire::ftp::proxy "http://example.com:8080/";
but leave the lines below in /etc/apt/apt.conf and /etc/apt/apt.conf.d/90no-proxy.conf as is to be useful for the next time.
- Acquire::http::proxy::server1.local "DIRECT";
- Acquire::http::proxy::server2.local "DIRECT";

What happened instead:
7. the three lines are removed and also "DIRECT" lines are removed.

Accepted ubuntu-system-service into oneiric-proposed, the package will build now and be available in a few hours. Please test and give feedback here. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you in advance!